Doctor Who Series 8: 15 Obscure Easter Eggs You Probably Missed

2. Cybermen Throwback (Dark Water/Death In Heaven)

OK, so this may not be the most obscure reference of all, but it's developed to such an extent that this list would be incomplete without it. The end of Dark Water sees Missy's brand of Cybermen unleashed on London, with the sliver soldiers seen pouring into the streets with St. Paul's Cathedral in the background. As the pre-release hype gleefully pointed out, this is a visual call-back to Second Doctor story The Invasion, which had near identical shots. But the links to previous Cybermen stories don't end there; The Tomb Of The Cybermen, another Second Doctor serial, featured a mausoleum full of the cyborgs as part of a deceptive plan, while the Master has used them in his schemes before. Death In Heaven continued the links to the past, with Kate Stewart revealing UNIT haven't just forgotten that attack, throwing a smashed, sixties-style cyber skull down as proof of The Invasion's events.